The abuse of power: The pervasive fallacy of power calculations for data analysis

It is well known that statistical power calculations can be valuable in pla nning an experiment. There is also a large literature advocating that power calculations be made whenever one performs a statistical test of a hypothe sis and one obtains a statistically nonsignificant result. Advocates of suc h post-experiment power calculations claim the calculations should be used to aid in the interpretation of the experimental results. This approach, wh ich appears in various forms, is fundamentally flawed. We document that the problem is extensive and present arguments to demonstrate the flaw in the logic.